The catechol estrogens have been isolated from human urine as major metabolites of estrone and estradiol. They have been shown to possess biological activity both in vivo and in vitro in several animal systems. The objectives of this proposal are: 1) to characterize the binding and biological activity of catechol estrogens in the rat uterus, hypothalamus and pituitary; 2) to detemine in rats the metabolism of and the tissue conversions of precursors to the catechol estrogens; 3) to characterize in humans the metabolism of and precursor conversions to the catechol estrogens; 4) to determine the amount of catechol estrogens produced in humans and their circulating levels and 5) to correlate all these data to estimate the possible physiological significance of these compounds to normal endocrinology in humans.